Injection fluid tuning

ABSTRACT

Injection fluid tuning is provided. In one possible implementation, injection fluid can be tuned by accessing both surface properties of rock found in a hydrocarbon reservoir of interest and a chemical composition of oil found in the reservoir of interest. An ion effect on wettability of a contact surface of the rock can be acquired and then used to formulate a tuned ion solution based on the ion effect on wettability of the contact surface of the rock. In another possible implementation, an electrolyte solution has an ionic composition and an ionic concentration configured to enhance recovery of oil from a reservoir. The electrolyte solution includes a content of direct contact ions including monovalent ions with a static polarizability larger than a preset limit sufficient to influence a contact surface of a rock in the reservoir to reach a desired wettability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional application of U.S. patentapplication Ser. No. 14/733580, filed Jun. 8, 2015, which is herebyincorporated herein by reference in its entirety

BACKGROUND

Current oilfield technologies can only produce a fraction of downholeoil associated with a well. For example, only 30% of the oil associatedwith an average well in the US can be produced. This means that 70% ofthe downhole oil associated with existing American wells (an estimated89 billion barrels) is still waiting to be produced.

Many organizations around the globe are currently looking into enhancedoil recovery (EOR) technologies to recover additional oil from existingwells. A variety of EOR technologies exist that can be tailored invarious combinations to increase production from individual reservoirs.

However, in the case of carbonate reservoirs, such tailoring efforts canbe complex, often involving extensive trial and error to determine aneffective blend of EOR technologies. Such trial and error can be timeconsuming and costly.

SUMMARY

Injection fluid tuning is provided. In one possible implementation,injection fluid can be tuned by accessing both surface properties ofrock found in a hydrocarbon reservoir of interest and a chemicalcomposition of oil found in the reservoir of interest. An ion effect onwettability of a contact surface of the rock can be acquired and thenused to formulate a tuned ion solution based on the ion effect onwettability of the contact surface of the rock.

In another possible implementation, an electrolyte solution has an ioniccomposition and an ionic concentration configured to enhance recovery ofoil from a reservoir. The electrolyte solution includes a content ofdirect contact ions including monovalent ions with a staticpolarizability larger than a preset limit sufficient to influence acontact surface of a rock in the reservoir to reach a desiredwettability.

In another possible implementation, a computer-readable tangible mediumincludes instruction that direct a processor to access one or moreproperties of a type of rock in a hydrocarbon reservoir. Instructionsare also present that direct the processor to acquire an ion effect onwettability of a contact surface of the rock and formulate a tuned ionsolution with a content of direct contact ions sufficient to increase awater wetness of the contact surface of the rock.

This summary is not intended to identify key or essential features ofthe claimed subject matter, nor is it intended to be used as an aid inlimiting the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the described implementations can be morereadily understood by reference to the following description taken inconjunction with the accompanying drawings.

FIG. 1 illustrates an example wellsite in which embodiments of injectionfluid tuning can be employed;

FIG. 2 illustrates an example computing device that can be used inaccordance with various implementations of injection fluid tuning;

FIG. 3 illustrates various ion effects on interfacial surface tension inaccordance with implementations of injection fluid tuning;

FIG. 4 illustrates various effects of ion pairing with surface groups inaccordance with implementations of injection fluid tuning;

FIG. 5 illustrates an example method associated with injection fluidtuning; and

FIG. 6 illustrates an example method associated with injection fluidtuning;

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of some embodiments of the present disclosure. However,it will be understood by those of ordinary skill in the art that thesystem and/or methodology may be practiced without these details andthat numerous variations or modifications from the described embodimentsmay be possible.

Additionally, some examples discussed herein involve technologiesassociated with the oilfield services industry. It will be understoodhowever that the techniques of Injection fluid tuning may also be usefulin a wide range of industries outside of the oilfield services sector,including for example, mining, geological surveying, medical imaging,etc.

As described herein, various techniques and technologies associated withinjection fluid tuning can facilitate the design of a tuned ion solutionconfigured to improve oil recovery from a reservoir by altering asurface wettability of rock in the reservoir and/or modifying a surfaceenergy between a crude oil and the tuned ion solution. In one possibleimplementation, the tuned ion solution can have a defined ion content.In another possible implementation, the tuned ion solution can have adefined ion content and a defined salinity.

In another possible implementation, an ion chemical composition andconcentration of ions in the tuned ion solution can be tailored for avariety of well/reservoir conditions, including, for example,temperature, pressure, chemical composition of oil in the reservoir,brine pH, rock geometry (including pore size distribution) and chemicalstructure of reservoir minerals, etc.

Example Wellsite

FIG. 1 illustrates a wellsite 100 in which embodiments of Injectionfluid tuning can be employed. Wellsite 100 can be onshore or offshore.In this example system, a borehole 102 is formed in a subsurfaceformation by rotary drilling in a manner that is well known. Embodimentsof Injection fluid tuning can also be employed in association withwellsites where directional drilling is being conducted.

A drill string 104 can be suspended within borehole 102 and have abottom hole assembly 106 including a drill bit 108 at its lower end. Thesurface system can include a platform and derrick assembly 110positioned over the borehole 102. The assembly 110 can include a rotarytable 112, kelly 114, hook 116 and rotary swivel 118. The drill string104 can be rotated by the rotary table 112, energized by means notshown, which engages kelly 114 at an upper end of drill string 104.Drill string 104 can be suspended from hook 116, attached to a travelingblock (also not shown), through kelly 114 and a rotary swivel 118 whichcan permit rotation of drill string 104 relative to hook 116. As is wellknown, a top drive system can also be used.

In the example of this embodiment, the surface system can furtherinclude drilling fluid or mud 120 stored in a pit 122 formed at wellsite100. A pump 124 can deliver drilling fluid 120 to an interior of drillstring 104 via a port in swivel 118, causing drilling fluid 120 to flowdownwardly through drill string 104 as indicated by directional arrow126. Drilling fluid 120 can exit drill string 104 via ports in drill bit108, and circulate upwardly through the annulus region between theoutside of drill string 104 and wall of the borehole 102, as indicatedby directional arrows 128. In this well-known manner, drilling fluid 120can lubricate drill bit 108 and carry formation cuttings up to thesurface as drilling fluid 120 is returned to pit 122 for recirculation.

Bottom hole assembly 106 of the illustrated embodiment can include drillbit 108 as well as a variety of equipment 130, including alogging-while-drilling (LWD) module 132, a measuring-while-drilling(MWD) module 134, a roto-steerable system and motor, various othertools, etc.

In one possible implementation, LWD module 132 can be housed in aspecial type of drill collar, as is known in the art, and can includeone or more of a plurality of known types of logging tools (e.g., anuclear magnetic resonance (NMR system), a directional resistivitysystem, and/or a sonic logging system). It will also be understood thatmore than one LWD and/or MWD module can be employed (e.g. as representedat position 136). (References, throughout, to a module at position 132can also mean a module at position 136 as well). LWD module 132 caninclude capabilities for measuring, processing, and storing information,as well as for communicating with surface equipment.

MWD module 134 can also be housed in a special type of drill collar, asis known in the art, and include one or more devices for measuringcharacteristics of the well environment, such as characteristics of thedrill string and drill bit. MWD module 134 can further include anapparatus (not shown) for generating electrical power to the downholesystem. This may include a mud turbine generator powered by the flow ofdrilling fluid 120, it being understood that other power and/or batterysystems may be employed. MWD module 134 can include one or more of avariety of measuring devices known in the art including, for example, aweight-on-bit measuring device, a torque measuring device, a vibrationmeasuring device, a shock measuring device, a stick slip measuringdevice, a direction measuring device, and an inclination measuringdevice.

Various systems and methods can be used to transmit information (dataand/or commands) from equipment 130 to a surface 138 of the wellsite100. In one implementation, information can be received by one or moresensors 140. The sensors 140 can be located in a variety of locationsand can be chosen from any sensing and/or detecting technology known inthe art, including those capable of measuring various types ofradiation, electric or magnetic fields, including electrodes (such asstakes), magnetometers, coils, etc.

In one possible implementation, sensors 140 receive information fromequipment 130, including LWD data and/or MWD data, which can be utilizedfor a variety of purposes including steering drill bit 108 and any toolsassociated therewith, characterizing a formation surrounding borehole102, characterizing fluids within wellbore 102, etc.

In one implementation a logging and control system 142 can be present.Logging and control system 142 can receive and process a variety ofinformation from a variety of sources, including equipment 130. Loggingand control system 142 can also control a variety of equipment, such asequipment 130 and drill bit 108.

Logging and control system 142 can also be used with a wide variety ofoilfield applications, including logging while drilling, artificiallift, measuring while drilling, wireline, etc. Also, logging and controlsystem 142 can be located at surface 138, below surface 138, proximateto borehole 102, remote from borehole 102, or any combination thereof.

Alternately, or additionally, information received by sensors 140 can beprocessed at one or more other locations, including any configurationknown in the art, such as in one or more handheld devices proximateand/or remote from the wellsite 100, at a computer located at a remotecommand center, in the logging and control system 142 itself, etc.

In one possible implementation, one or more injection wells similar toborehole 102 can exist in proximity to wellsite 100. Injection fluids,such as the tuned ion solution disclosed herein, can be injected intothese adjacent wells such that the injection fluid can migrate throughreservoir 144 to borehole 102, improving production of oil fromreservoir 144 into wellbore 102.

Example Computing Device

FIG. 2 illustrates an example device 200, with a processor 202 andmemory 204 for hosting a tuning module 206 configured to implementvarious embodiments of injection fluid tuning as discussed in thisdisclosure. Memory 204 can also host one or more databases and caninclude one or more forms of volatile data storage media such as randomaccess memory (RAM), and/or one or more forms of nonvolatile storagemedia (such as read-only memory (ROM), flash memory, and so forth).

Device 200 is one example of a computing device or programmable device,and is not intended to suggest any limitation as to scope of use orfunctionality of device 200 and/or its possible architectures. Forexample, device 200 can comprise one or more computing devices,programmable logic controllers (PLCs), etc.

Further, device 200 should not be interpreted as having any dependencyrelating to one or a combination of components illustrated in device200. For example, device 200 may include one or more of a computer, suchas a laptop computer, a desktop computer, a mainframe computer, etc., orany combination or accumulation thereof.

Device 200 can also include a bus 208 configured to allow variouscomponents and devices, such as processors 202, memory 204, and localdata storage 210, among other components, to communicate with eachother.

Bus 208 can include one or more of any of several types of busstructures, including a memory bus or memory controller, a peripheralbus, an accelerated graphics port, and a processor or local bus usingany of a variety of bus architectures. Bus 208 can also include wiredand/or wireless buses.

Local data storage 210 can include fixed media (e.g., RAM, ROM, a fixedhard drive, etc.) as well as removable media (e.g., a flash memorydrive, a removable hard drive, optical disks, magnetic disks, and soforth).

One or more input/output (I/O) device(s) 212 may also communicate via auser interface (UI) controller 214, which may connect with I/O device(s)212 either directly or through bus 208.

In one possible implementation, a network interface 216 may communicateoutside of device 200 via a connected network, and in someimplementations may communicate with hardware, such as one or moresensors 140, etc.

In one possible embodiment, sensors 140 may communicate with system 200as input/output device(s) 212 via bus 208, such as via a USB port, forexample.

A media drive/interface 218 can accept removable tangible media 220,such as flash drives, optical disks, removable hard drives, softwareproducts, etc. In one possible implementation, logic, computinginstructions, and/or software programs comprising elements of tuningmodule 206 may reside on removable media 220 readable by mediadrive/interface 218.

In one possible embodiment, input/output device(s) 212 can allow a userto enter commands and information to device 200, and also allowinformation to be presented to the user and/or other components ordevices. Examples of input device(s) 212 include, for example, sensors,a keyboard, a cursor control device (e.g., a mouse), a microphone, ascanner, and any other input devices known in the art. Examples ofoutput devices include a display device (e.g., a monitor or projector),speakers, a printer, a network card, and so on.

Various processes of tuning module 206 may be described herein in thegeneral context of software or program modules, or the techniques andmodules may be implemented in pure computing hardware. Softwaregenerally includes routines, programs, objects, components, datastructures, and so forth that perform particular tasks or implementparticular abstract data types. An implementation of these modules andtechniques may be stored on or transmitted across some form of tangiblecomputer-readable media. Computer-readable media can be any availabledata storage medium or media that is tangible and can be accessed by acomputing device. Computer readable media may thus comprise computerstorage media. “Computer storage media” designates tangible media, andincludes volatile and non-volatile, removable and non-removable tangiblemedia implemented for storage of information such as computer readableinstructions, data structures, program modules, or other data. Computerstorage media include, but are not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, digital versatile disks (DVD)or other optical storage, magnetic cassettes, magnetic tape, magneticdisk storage or other magnetic storage devices, or any other tangiblemedium which can be used to store the desired information, and which canbe accessed by a computer.

Example System(s)

Surface wettability of rocks in a reservoir, such as reservoir 144, canbe a factor in oil production. For example, more than 80% of carbonaterock formations are moderate to strongly oil-wet. In one possibleimplementation, a rock surface can become oil-wet (or more oil-wet)through adsorption of polar compounds, such as those found in oil. Polarcompounds can include, for example, carboxylic acids, naphthenic acids,asphaltenes, etc. In some instances, adsorption of polar compounds canalter the originally hydrophilic properties of a rock surface to a morehydrophobic nature. This can lower oil relative permeability and resultin poor displacement efficiency of oil in the reservoir.

FIG. 3 illustrates various ion effects on interfacial surface tension inaccordance with implementations of injection fluid tuning. Graphs 302and 304 plot ion concentration (vertical axis) versus perpendiculardistance from a contact surface 306 (horizontal axis). Ion concentrationcan be measured and/or represented in any units possible, including, forexample, moles/liter, etc. In one possible implementation, contactsurface 306 can include the surface of a rock in reservoir 144,including, for example, the inside of a pore, fissure, crack, etc. Inanother possible implementation, contact surface 306 can include anycompartment where ion concentration is low and/or close to zero(including, for example, a non-polar fluid such as oil, etc.).

Graph 302 illustrates a condition in which an ion concentration atcontact surface 306 is enriched in comparison to an average bulk valueion concentration 310 in a fluid contacting contact surface 306. Graph304 illustrates a depletion of ion concentration at contact surface 306in comparison to average bulk value ion concentration 310 in a fluidcontacting contact surface 306.

Molecular-scale pictures 312, 314 illustrate ion distribution at aninterfacial layer 320 defined by contact surface 306 and a tuned ionsolution 322 in contact with contact surface 306. In one possibleimplementation, tuned ion solution fluid 322 can be engineered to affecta wettability of contact surface 306. In another possibleimplementation, tuned ion solution fluid 322 can be engineered to affecta level of interfacial energy between oil and tuned ion solution 322. Inyet another possible implementation, tuned ion solution fluid 322 can beengineered to affect a wettability of contact surface 306 and a level ofinterfacial energy between oil and tuned ion solution 322. It will beunderstood that in some implementations, well fluids (including oil,water, etc.) may also be present in, and/or in addition to, tuned ionsolution 322.

In one possible implementation, tuned ion solution 322 can be an aqueoussolution engineered to have a specific ionic composition with a specificcontent of ions. For example, in one possible embodiment, a specificcontent of direct contact ions suitable for making direct contact withcharged groups of ions on contact surface 306 can be present toencourage the creation of a water-wet condition on contact surface 306.Interfacial properties of ions (including, for example, their surfaceaffinity) can depend on a polarizability of the ions. Therefore, in onepossible embodiment, direct contact ions can include any anions withstatic polarizability larger than 3.4×10⁻³⁰ m³ and/or any cations withstatic polarizability larger than 1.9×10⁻³⁰ m³. For instance, directcontact ions can include any cations and/or anions larger than achloride ion, such as, for example, bromide ions, iodide ions, etc.

In another possible embodiment, a specific content of non-contact ionsengineered to stay separated from charged groups of ions on contactsurface 306, can be present, such that a wetness condition of contactsurface 306 is not affected by tuned ion solution 322.

In one possible aspect, tuned ion solution 322 can also have anengineered salinity range.

Tuned ion solution 322 can be placed in contact with contact surface 306through various techniques, including water flooding.

As shown in graph 302 and picture 312, in one possible implementation,if a concentration of ions 324 in fluid 322 is enriched at interface 320compared to an average concentration of the ions 324 in bulk value 310,a decrease in surface tension can result.

In another possible implementation, as shown in graph 304 and picture314, if ions 324 are depleted from contact surface 306 compared to anaverage bulk concentration of ions 324 in bulk value 310, an increase insurface tension can result.

In some possible implementations, surface wettability of contact surface306 can act to restrict access and/or cause earlier water breakthroughto oil reserves in reservoir 144. In one possible embodiment,oil-wetness of contact surface 306 can be overcome by directly alteringone or more surface properties of the rock to make contact surface 306water-wet. This can reduce drag forces and capillary number, supportingwater imbibition into pores in the rock by positive capillary pressure,thus improving oil recovery from reservoir 144.

In one possible implementation, injection of tuned ion solution 322 intoreservoir 144 can reduce a concentration of adsorbed polar species (suchas carboxylic acids, asphaltenes, etc.) on contact surface 306 inreservoir 144, including rock surfaces within pore matrices.

Injection of tuned ion solution 322 into reservoir 144, can also reducea possibility of further polar species adsorption by rock in reservoir144. In one possible aspect, this can increase a mobility of oil in aformation in reservoir 144 due to wettability alteration of surfaces 306in the formation from oil-wet to water-wet, allowing the oil to be moreeasily removed from pores in the rock.

In one possible embodiment, a combination of ions in tuned ion solution322 can lead to “cooperative work” of ions 324 in altering a wettabilityof a mineral, such as, for example, calcite. For example, affinitiesbetween materials such as sulfate, calcium, magnesium, sodium, etc., canchange a morphology of contact surface 306 when the materials arepresent in various ratios.

In one possible embodiment, a tuned ion solution 322 with a low salinity(such as, for example, 5 kppm of monovalent ions and 1 kppm of similarmonovalent ions) can encourage recovery of oil from rock in reservoir144. In one possible aspect, tuned ion solution 322 can include a brinemixture with a low salinity along with an engineered content of directcontact ions to create conditions on contact surface 306 that are moreamenable to increasing recovery of oil from reservoir 144 by helping tomobilize residual oil in the rock within reservoir 144.

In one possible embodiment, the effect of a particular ion compositionon an interfacial surface tension of tuned ion solution 322 can beassociated with adsorption or desorption of ions at interface 320 oftuned ion solution 322 and contact surface 306. For instance, differentionic species in tuned ionic solution 322 can influence interfacialsurface tension of polar and non-polar fluids and theirmixtures/dispersions in various ways. For example direct contact ionscan decrease surface tension while non-contact ions can increase surfacetension. In one possible aspect, factors such as temperature, pressure,chemical composition, pH of tuned ion solution 322 in which the ions 324are found, concentration of ions 324 and overall chemical composition oftuned ion solution 322, etc., can also have an effect on the surfacetension.

In one possible embodiment, ion adsorption/desorption can be influencedby an affinity of ions 324 to interface 320 as well as an affinity ofions 324 to specific chemical groups on contact surface 306. In oneaspect, charges of chemical groups on contact surface 306 can contributeto this influence.

In one possible implementation, some ions 324 can make direct ion pairswith chemical groups on contact surface 306. In one aspect, aconcentration of ions 324 on contact surface 306 can be enriched inproportion to the chemical groups available on contact surface 306.Other ions 324 may not be able to make a direct ion pair due to solventeffects (for example, polar solvents may interact with charged chemicalgroups on contact surface 306 leading to a desolvation penalty).

FIG. 4 illustrates various effects of ion pairing with surface groups inaccordance with implementations of injection fluid tuning. In onepossible implementation, such as shown in illustration 402, direct ionpair formation can occur when direct contact ions 404 in tuned ionsolution 322 exhibit a strong enough affinity to ions 406 at contactsurface 306 to make direct contact with ions 406. In such a case, directcontact ions 404 can come from tuned ion solution 322 and substitutesolvent at the charged ions 406.

In another possible implementation, such as shown in illustration 408,solvent-separated ion interactions can result when non-contact ions 410in tuned ion solution 322 exhibit a low enough affinity to ions 406 atcontact surface 306 such that the non-contact ions 410 stay in solutionand do not substitute solvent at the ions 406. It will be understoodthat non-contact ions 410, direct contact ions 404, as well as ions 406at contact surface 306 may be of any polarity, and not just those shownin FIG. 4. Moreover non-contact ions 410 and direct contact ions 404 cancomprise ions 324.

In one possible implementation, ion effects on interfacial surfacetension can be determined by one or more of ion-ion, ion-fluid,fluid-surface and ion-surface interactions. In one possibleimplementation, the variety of ion effects on interfacial propertiesthat can influence oil/water wettability of contact surface 306 caninclude, for example:

-   1) adsorption/desorption of ions 324;-   2) Ion exchange at interface 320 (i.e. ions 324 from solution 322    can substitute ions 406 on contact surface 306, which can lead to    alteration of properties of contact surface 306);-   3) Formation of salt bridges between charged groups (comprised of    groups of ions 406) on contact surface 306 and charged groups of oil    components (such as ions in a solution including hydrocarbons);-   4) Local change of a pH level at contact surface 306 (for example,    adsorption of ions 324 at contact surface 306 can influence water    dissociation at contact surface 306, changing a local concentration    of H+ and OH− ions). In such an instance, local changes of pH can    lead to different protonation states of oil components at contact    surface 306 (including compounds with carboxylic groups such as    asphaltenes). In some instances, this can alter the oil wetting    properties of contact surface 306;-   5) Ions 324 can compete with water and surface charged groups of    ions 406 for charged or polar groups of oil components (e.g.    carboxylic groups). Competitive binding of ions 324 to these    chemical groups of oil components can change a free energy of    binding of the oil components to contact surface 306. In some    instances, this can alter the oil wettability of contact surface    306.

In one possible implementation, an overall net effect of ions 324 onwetting properties of a particular combination of oil and tuned ionsolution 322 and contact surface 306 can result from a combination ofone or more of the effects listed above. However, in some embodiments,one or two of the effects listed above will be dominant in changing theinterfacial properties of the system. In one possible implementation,such dominant effect(s) can result from changes of a composition of ions324 in fluid 322.

In one possible implementation, an ion composition of tuned ion solution322 (in terms of types of ions 324 and their concentrations) can berationally designed and tailored for a particular reservoir ofmineral/rock.

In one possible implementation, ion effects on interfacial surfacetension and overall rheological properties of fluids in porous media canbe determined by a balance of ion-ion, ion-fluid, fluid-surface andion-surface interactions. Such parameters can be influenced by (1)chemical ion composition of the fluid; (2) ion concentration in thefluid. Thus, tuned ion solution 322 can be engineered to have an ioncomposition (chemical nature of ions and their concentration) to achievea variety of results, including improving crude oil recovery fromreservoir 144. This can be achieved by one or more of the following:

-   -   Modification of interfacial tension between tuned ion solution        322 and oil; and/or tuned ion solution 322 and surface 306;        and/or oil and surface 306;    -   Modification of rheological properties of tuned ion solution 322        in porous reservoir media;    -   Improving stability of emulsions of tuned ion solution 322 and        oil; and    -   Modifying wetting properties of tuned ion solution 322 with        regard to oil and contact surface 306.

Example Methods

FIGS. 5-6 illustrate example methods for implementing aspects ofInjection fluid tuning. The methods are illustrated as a collection ofblocks and other elements in a logical flow graph representing asequence of operations that can be implemented in hardware, software,firmware, various logic or any combination thereof. The order in whichthe methods are described is not intended to be construed as alimitation, and any number of the described method blocks can becombined in any order to implement the methods, or alternate methods.Additionally, individual blocks and/or elements may be deleted from themethods without departing from the spirit and scope of the subjectmatter described therein. In the context of software, the blocks andother elements can represent computer instructions that, when executedby one or more processors, perform the recited operations. Moreover, fordiscussion purposes, and not purposes of limitation, selected aspects ofthe methods may be described with reference to elements shown in FIGS.1-4.

FIG. 5 illustrates an example method 500 that can be employed to createa tuned ion solution, such as tuned ion solution 322, to alter a wetnessof a surface, such as contact surface 306, and/or affect a level ofinterfacial energy between oil and the tuned ion solution.

At block 502, surface properties, such as properties of contact surface306, of rock found in a hydrocarbon reservoir of interest, such asreservoir 144, are accessed. In one possible embodiment, the surfaceproperties can be surface properties of a rock and/or a compartmentwhere ion concentration is low and/or close to zero (such as, forexample, a non-polar fluid such as oil, etc.). In one implementation,the surface properties can be accessed from a database of existinginformation. Alternately, the surface properties can be accessed byobtaining various samples from the reservoir.

In one possible embodiment, the surface properties can include a widevariety of geometrical and chemical properties of a rock in thereservoir including, for example, nature and concentration of chargedgroups on the surface, nano/micro scale roughness of the surface, etc.

In one possible implementation, techniques that can be used to examinerock properties include characterization experiments such as atomicforce microscopy (AFM) techniques, x-ray photoelectron spectroscopy(XPS) techniques, surface Raman and other surface sensitive techniques,mass spectrometry and other analytical chemistry tools (to determine achemical composition of the surface for example), crystallographic tools(such as X-ray diffraction etc.), to determine a structure of therock/minerals, etc.

Calculations can be also used to examine rock properties. These caninclude, for example, molecular mechanics methods and quantum mechanicsmethods to interpret experimental results and refine a molecular-levelstructure of a surface of the rock.

In one possible implementation, one or more of the actions associatedwith this block 502 can be performed on the most abundant rock mineralin the reservoir.

At block 504, a chemical composition of oil found in the reservoir ofinterest can be accessed. In one possible implementation, the chemicalcomposition of the oil (including, for example, concentrations andstructures of compounds in the oil) can be accessed from a database ofexisting information. Alternately, the chemical composition of the oilcan be accessed by obtaining various samples of the oil from thereservoir and performing various analyses.

In one possible implementation, the chemical composition of the oil caninclude information regarding compounds with charged and polar chemicalgroups (such as asphaltenes, aromatic and poly-aromatic carboxylic acidsetc.) in the oil. In one possible aspect, the chemical composition ofthe oil can also include information regarding concentrations andstructures of the compounds with charged and polar chemical groups.Various analytical chemistry and physical methods can be used for thesepurposes, including, for example, mass spectroscopy, Raman, infrared andvis-UV spectroscopy, chromatography etc.

At block 506, an ion effect on wettability of a contact surface of therock, such as contact surface 306, is acquired. For example, in onepossible implementation, one or more dominant ion effects on oil/waterwettability of the surface can be determined. A combination ofexperimental techniques (including, for example, interfacial tensionmeasurements, contact angle measurements, measurements of fluid flow,etc.) can be used for these purposes and be combined with molecularmechanics and/or quantum chemistry calculations.

In one possible embodiment, screening all possible combinations of ionscan be avoided in favor of a search for a limited number of dominanteffects. In one possible aspect this can be accomplished through testingof pairs of ions with differences in their properties such as e.g. smallions—large ions; low charge density ions—high charge density ions;monovalent ions—multivalent ions; etc. In some cases, such tests of ionpairs with differences in their properties can allow for a moreexpedient determination of one or more dominant effects of ions on thewettability properties of the mixture of oil and the tuned ion solutionat the particular rock interface.

At block 508, a tuned ion solution can be formulated based on the ioneffect on wettability of the contact surface of the rock to tune one ormore surface properties of the rock as desired. Alternately, oradditionally, in one possible implementation, the tuned ion solution canbe formulated to tune interfacial properties between the oil and thetuned ion solution as desired. In one possible aspect, this can beaccomplished by using the chemical composition of oil in the reservoirto determine an ion effect on an interfacial tension between the oil andthe tuned ion solution. In such a manner a surface energy between theoil and the tuned ion solution can be increased and/or decreased asdesired.

For example, in one possible embodiment, some or all of the results fromblocks 502-506 can be used to engineer the tuned ion solution to affectinterfacial properties of the rock-oil-tuned ion solution system in adesired way. Samples of reservoir fluid and reservoir rock can be usedas can various experimental and/or computational models associated withthe reservoir fluid and the reservoir rocks. In one possible embodiment,reservoir fluid includes any fluid found in the reservoir, such aswater, oil, etc.

In another possible implementation, if ion exchange is desired, variousions can be added to the tuned ion solution to modify the properties ofthe contact surface. For instance, if the ions from the tuned ionsolution that substitute for the surface ions have higher charge densitythan the surface ions they substitute, then the surface can become morepolar and more water-wet. Alternatively, if the ions from the tuned ionsolution that substitute for the surface ions have lower charge densitythan the surface ions they substitute, then the surface could becomeless polar and less water-wet.

In another possible implementation, if the formation of salt bridges isdesired, ions can be added to the tuned ion solution that are effectivein formation of salt bridges between charged groups on the surface andcharged groups of oil components. This can increase oil wettability ofthe surface and in some cases block capillary pores through formation ofsupramoleculer aggregates on the surface from components of the oilbeing bound by the salt bridges.

If increased oil wettability is not desired, then in another possibleimplementation, various ions (such as, for example, Ca²⁺) known to beactive in terms of forming salt bridges (‘bridge-active’ ions) can beremoved from the tuned ion solution. In one possible aspect, removedbridge active ions can be replaced in the tuned ion solution with ionsthat are passive in terms of forming the salt bridges (such as, forexample, K⁺).

In instances when removing one or more bridge active ions is notpossible (e.g. the bridge active ions are already present in thereservoir fluid) the effect of the bridge active ions can be inhibitedby adding chelating agents (i.e. chemicals that bind the bridge-activeions) such as, for example, citric acid, ethylenediaminetetraacetic acidor its sodium salt, etc., to the tuned ion solution.

In another possible implementation, if a local change of pH level isdesired, then the pH of the tuned ion solution can be changed by addingacids (including inorganic acids such as HCl and/or organic acids likeacetic acid, citric acid, etc.) or adding bases such as KOH, NaOH, etc.

In one possible embodiment, the nature of the counter-ions of the acids(anions) and bases (cations) can be taken into account while tuning thepH of the tuned ion solution. For example, K+ ions have a lower chargedensity than Na+ ions, and, consequently have lower binding affinity tocarboxylic groups. Therefore, KOH at the same molar concentration asNaOH would lead to a lower rate of bridging together oil components withcarboxylic groups.

In yet another possible embodiment, if competitive binding of ions tocharged and/or polar groups is desired, ions can be added to the tunedion solution that competitively bind the surface or oil componentsgroups to prevent formation of supramolecular aggregates. In onepossible aspect, this can decrease an affinity of oil components to thesurface making the surface less oil-wet.

In one possible implementation, effects of tuning the tuned ion solutioncan be tested, for example using a test bed system. This can be doneusing a wide variety of techniques, including spontaneous imbibition,core flooding, interfacial tension measurements, wettabilitymeasurements, zeta potential measurements, etc.

FIG. 6 illustrates an example method 600 that can be employed to createa tuned ion solution, such as tuned ion solution 322, to alter a wetnessof a surface, such as contact surface 306.

At block 602, one or more properties of rock in a hydrocarbon reservoir,such as reservoir 144, can be accessed. In one implementation, theseproperties can be accessed from a database of existing information.Alternately, the properties can be accessed by obtaining various samplesfrom the reservoir.

In one possible embodiment, various properties of a rock surface presentin the reservoir can be examined. These properties can include a widevariety of geometrical and chemical properties including, for example,nature and concentration of charged groups on the surface, nano/microscale roughness of the surface, etc.

In one possible implementation, techniques that can be used to examinerock properties include experiments such as AFM, XPS, surface Raman andother surface sensitive techniques, mass spectrometry and otheranalytical chemistry tools (to determine a chemical composition of thesurface for example), crystallographic tools (such as X-ray diffractionetc.), to determine a structure of the rock/minerals, etc. Calculationscan be used to examine rock properties. These can include, for example,molecular mechanics methods and/or quantum mechanics methods tointerpret experimental results and refine a molecular-level structure ofa surface of the rock.

In one possible implementation, one or more of the actions associatedwith this block 602 can be performed on the most abundant rock mineralin the reservoir.

At block 604, an ion effect on wettability of a surface of the rock canbe acquired. In one possible implementation, one or more dominant ioneffects on oil/water wettability of the rock surface can be determined.In one aspect, a combination of experimental techniques (including, forexample, interfacial tension measurements, contact angle measurements,measurements of fluid flow, etc.) can be used for these purposes and becombined with molecular mechanics and quantum chemistry calculations.

In one possible embodiment, screening all possible combinations of ionscan be avoided in favor of a search for a limited number of dominanteffects that can be carried out through testing of pairs of ions withdifferences in their properties such as e.g. small ions—large ions; lowcharge density ions—high charge density ions; monovalentions—multivalent ions; etc. In some cases, such tests of ion pairs withdifferences in their properties can allow for a more expedientdetermination of one or more dominant effects of ions on the wettabilityproperties of the mixture of oil and the tuned ion solution at theparticular rock interface.

At block 606, a tuned ion solution is formulated with a content ofdirect contact ions sufficient to increase a water wetness of thesurface of the rock. For example, in one possible embodiment, some orall of the results from blocks 602-604 can be used to engineer the tunedion solution to affect interfacial properties of the rock-oil-tuned ionsolution system in a desired way. Samples of reservoir fluid andreservoir rock can be used as can various experimental and/orcomputational models associated with the reservoir fluid and thereservoir rocks. In one possible embodiment, reservoir fluid includesany fluid found in the reservoir, such as water, oil, etc.

Although a few embodiments of the disclosure have been described indetail above, those of ordinary skill in the art will readily appreciatethat many modifications are possible without materially departing fromthe teachings of this disclosure.

Accordingly, such modifications are intended to be included within thescope of this disclosure as defined in the claims.

1. A tuned ion solution comprising: an electrolyte solution having anionic composition and an ionic concentration configured to enhancerecovery of oil from a reservoir, wherein the electrolyte solutionincludes a content of direct contact ions including monovalent ions witha static polarizability larger than a preset limit sufficient toinfluence a contact surface of a rock in the reservoir to reach adesired wettability.
 2. The tuned ion solution of claim 1, wherein theconcentration of direct contact ions in the electrolyte solution is lessthan 20000 parts per million.
 3. The tuned ion solution of claim 1,wherein the preset limit includes monovalent anions with staticpolarizability larger than 3.4×10⁻³⁰ m³.
 4. The tuned ion solution ofclaim 1, wherein the preset limit includes monovalent cations withstatic polarizability larger than 1.9×10⁻³⁰ m³.
 5. The tuned ionsolution of claim 1, wherein the ionic composition and the ionicconcentration are further configured to modify a surface energy betweenoil and the tuned ion solution as desired.
 6. The tuned ion solution ofclaim 1, wherein the content of direct contact ions includes one or moreof: bromide ions; iodide ions; and nitrate ions.
 7. A computer-readabletangible medium with instructions stored thereon that, when executed,direct a processor to perform acts comprising: accessing one or moreproperties of a type of rock in a hydrocarbon reservoir; acquiring anion effect on wettability of a contact surface of the rock; andformulating a tuned ion solution with a content of direct contact ionssufficient to increase a water wetness of the contact surface of therock.
 8. The computer-readable medium of claim 7, further includinginstructions to direct a processor to perform acts comprising: accessingone or more properties of the type of rock found in the hydrocarbonreservoir by interpreting experimental results and refining a molecularlevel structure of the contact surface of the rock using one or more of:molecular mechanics; and quantum mechanics
 9. The computer-readablemedium of claim 7, further including instructions to direct a processorto perform acts comprising: accessing one or more properties of the typeof rock in the hydrocarbon reservoir by querying a database.
 10. Thecomputer-readable medium of claim 7, further including instructions todirect a processor to perform acts comprising: acquiring the ion effecton wettability of the contact surface of the rock by combiningexperimental data with one or more of: molecular mechanics studies; andquantum chemistry calculations.
 11. The computer-readable medium ofclaim 7, further including instructions to direct a processor to performacts comprising: formulating the tuned ion solution with a content ofdirect contact ions sufficient to increase the water wetness of thecontact surface of the rock by performing calculations on computationalmodels of one or more of: the tuned ion solution; and the rock.